processOneFromEnv now catches buffer.pop() failures so one env's hiccup
doesn't reject Promise.all and bubble up to the loop's outer catch. The
polling loop itself wraps each runOnce in try/catch and backs off with
capped exponential delay (up to 5s) instead of exiting permanently on the
first listEnvs/pop error. Stop semantics are unchanged: only the stopping
flag breaks the loop.
Adds two regression tests using a stub buffer (no Redis container) so
fault injection is deterministic.
Dan Sutton
d76bb9e4ea